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Tribocorrosion in shoulder arthroplasty humeral component retrievals
J Shoulder Elbow Surg (2015) -, 1-5
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Tribocorrosion in shoulder arthroplasty humeral component retrievals Matthew G. Teeter, PhDa,b,c, Michael J. Carroll, MD, FRCSCd, Gilles Walch, MDe, George S. Athwal, MD, FRCSCa,d,* a
Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada b Department of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada c Surgical Innovation Program, Lawson Health Research Institute, London, ON, Canada d Roth j McFarlane Hand and Upper Limb Centre, St. Joseph’s Health Care, London, ON, Canada e H^ opital Prive Jean Mermoz, Generale de Sante, Centre Orthopedique Santy, Lyon, France Background: Tribocorrosion at the modular taper connections of total hip implants has been associated with trunnionosis and adverse local tissue reactions. Modularity is also widely used in shoulder arthroplasty implants, but little information exists about the potential for tribocorrosion. This study hypothesized that there would be mild or no tribocorrosion in a series of retrieved shoulder implants. Methods: A total of 28 implants with a mean implantation time of 6.2 6.0 years were evaluated using a validated damage scoring method. Implant tapers on the head and stem were divided into upper (deepest) and lower zones and independently scored for fretting and corrosion damage from 1 (none) to 4 (severe). Results: Corrosion was present on 32% of heads and 38% of stems, whereas fretting was present on 36% of heads and 46% of stems. There was significantly greater (P ¼ .02) corrosion in the lower zone of the retrieved stems (1.4 0.5) than there was in the upper zone (1.1 0.3). Correlation between the head and stem corrosion for lower zone was moderate (r ¼ 0.41; P ¼ .04). Discussion: Tribocorrosion was present on the heads and stems of some of the retrieved shoulder implants examined in this study. The incidence of tribocorrosion in shoulder implants was lower than in reported cases of retrieved hip implants. The greatest damage was in the lower zone of the taper, where the connection may be exposed to the surrounding joint fluid. It remains to be seen whether this leads to any clinical presentation of trunnionosis. Level of evidence: Basic Science Study, Implant Retrieval. Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Shoulder arthroplasty; humeral component; revision; tribocorrosion; fretting; corrosion; trunnionosis; retrieval
Investigations performed at the Implant Retrieval and Analysis Laboratory, University of Western Ontario, London, ON, Canada. IRB approval was not required for this study. *Reprint requests: George S. Athwal, MD, FRCSC, Roth j McFarlane Hand and Upper Limb Centre, St. Joseph’s Health Care, 268 Grosvenor St, London, ON N6A 4L6, Canada. E-mail address: [email protected] (G.S. Athwal).
Modularity in joint replacement implants enables the arthroplasty surgeon to customize the fit of an implant to the patient intraoperatively. Recently, the modular connectors between implant components have been identified as a source of corrosion and debris, leading to so-called trunnionosis.2-4,7,9 Trunnionosis is the term used to describe
1058-2746/$ - see front matter Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2015.07.004
2 the clinical symptoms caused by tribocorrosion, which is damage to the Morse taper connections of modular joint replacements. This damage is made up of fretting, seen as scars in the metal surface, and corrosion, seen as black debris. First identified with metal-on-metal total hip implants, tribocorrosion in taper junctions has now also been identified in metal-on-plastic total hip implants and in modular total knee replacement.1,12 Many different factors are thought to be associated with tribocorrosion, including head size, head offset, head angle, flexural rigidity of the neck, dissimilar alloy pairings, and dimensions of the modular taper connection itself.7 Modularity is also widely used in shoulder arthroplasty implants. However, retrieval studies of shoulder implants are much sparser in the literature than for hip or knee implants. Cusick et al5 studied dissociation of reverse total shoulder replacement implants and were able to evaluate 5 retrieved implants using tribocorrosion damage scoring. Four of the 5 implants had no signs of fretting or corrosion at the modular connection, and 1 implant had mild fretting and corrosion. In this 1 implant, the corrosion was only a small area of damage and did not cause any permanent deformation of the taper. Our institution has a long-running implant retrieval program for the hip and the knee and has subsequently expanded to include the shoulder. We have used our retrieval program to evaluate tribocorrosion of hip implants associated with factors such as dual-modular stems, trunnion size, and head length. The purpose of this study was to evaluate the presence of tribocorrosion in retrieved humeral total and hemiarthroplasty modular implants. We hypothesized that we would see mild or no corrosion or fretting damage at the modular connections of shoulder arthroplasty retrieval implants.
Methods Twenty-eight implants explanted by 2 shoulder surgeons (G.S.A., G.W.) were available for analysis. All implants were used in anatomic total shoulder arthroplasty or hemiarthroplasty. The implants had a mean implantation time of 6.2 6.0 years (range, 0.4-21 years). Implants were used in 11 male patients and 17 female patients. The primary reason for revision was glenoid or humeral component loosening for 11 cases, rotator cuff tear for 8 cases, infection for 5 cases, instability for 2 cases, and pain and malpositioning for 1 case each. No cases were revised for known trunnionosis. The implant models included Aequalis (Tornier, Bloomington, MN, USA; n ¼ 13), Bigliani/Flatow (Zimmer, Warsaw, IN, USA; n ¼ 3), Univers II (Arthrex, Naples, FL, USA; n ¼ 2), AP (DePuy, Warsaw, IN, USA; n ¼ 2), Eclipse (Arthrex; n ¼ 1), Bio-Modular (Biomet, Warsaw, IN, USA; n ¼ 1), Nano (Biomet; n ¼ 1 ), TESS (Biomet; n ¼ 1), Unite (DePuy; n ¼ 1), Reunion (Stryker, Kalamazoo, MI, USA; n ¼ 1), Solar (Stryker; n ¼ 1), and Sidus (Zimmer; n ¼ 1). All models included a cobalt-chromium humeral head and a titanium humeral stem or anchor.
M.G. Teeter et al.
Figure 1 Diagram of a shoulder replacement implant, showing the upper and lower zones that were assigned to the modular connectors of the head and stem (inset).
The visual damage classification score for fretting and corrosion described by Goldberg et al8 was used for this study. This classification is the most commonly used damage scoring system to identify tribocorrosion on retrieved implants. Fretting and corrosion are scored independently, ranging from 1 (none) to 4 (severe). For corrosion, a mild score of 2 represents <30% of the taper surface being discolored or dull, whereas a moderate score of 3 represents discoloration of >30% of the surface or the presence of black debris, pits, or etch marks over <10% of the surface. A severe corrosion score of 4 represents >10% of the surface containing black debris, pits, or etch marks. For fretting, a mild score of 2 represents bands of scars involving 3 or fewer machine lines, and a moderate score of 3 represents the involvement of >3 machine lines. A severe score of 4 involves several bands of scars across multiple adjacent machine lines or flattened areas with nearby scars. Iatrogenic damage from implantation or explantation was identified and excluded from the tribocorrosion assessment. Two observers analyzed each retrieved implant independently and recorded a score using the damage scale. In the case of a scoring discrepancy, both observers reanalyzed the implant and decided on a mutually agreeable value. All analyses were performed using a stereomicroscope (SZ-CTV; Olympus, Tokyo, Japan). The modular connections of the head and stem were divided in half into upper and lower zones, representing the deepest and most exposed regions of the taper connections, respectively (Fig. 1). Therefore, for each implant, a total of 8
Tribocorrosion in shoulder arthroplasty
3
scores were assigned: a fretting score and corrosion score for the upper and lower zones for both the head and the stem. Two implants used a separate connector part between the head and the stem, for which an additional 4 scores were recorded (fretting and corrosion scores for the head side and the stem side). In 1 case, the stem had a female taper, whereas in all other instances, the stem had a male taper. In a minority of cases (n ¼ 4), only the humeral heads were explanted and the stems remained in situ and therefore were unavailable. Descriptive statistics were calculated for all measurements. A D’Agostino and Pearson normality test revealed a non-Gaussian distribution for the data. Therefore, a Wilcoxon matched-pairs signed rank test was used to compare values for fretting and corrosion between zones, and the Spearman rank correlation coefficient was used for correlations between values. A P value of <.05 was considered significant. All statistical analysis was performed with Prism version 6.0 (GraphPad Software Inc., La Jolla, CA, USA).
Results Corrosion was present (score of 2) on 9 of the 28 heads (32%) and 9 of the 24 stems (38%). There was significantly greater (P ¼ .02) corrosion in the lower zone of the retrieved stems (1.4 0.5; range, 1-2) than there was in the upper zone (1.1 0.3; range, 1-2). However, there was no difference (P ¼ 1.0) in corrosion scores between the upper and lower zones of the retrieved heads (both zones 1.4 0.8; range, 1-4). The correlation for lower zone corrosion between the head and stem was moderate (r ¼ 0.41; P ¼ .04); but for the upper zone, it was insignificant (r ¼ 0.10; P ¼ .63). There were no significant correlations between corrosion scores and implantation time (P ¼ .10 for the head, P ¼ .31 for the stem) or for patient gender (P ¼ .17 for the head, P ¼ .54 for the stem). Fretting was present (score of 2) on 10 of the 28 heads (36%) and 11 of the 24 stems (46%). There was no significant difference (P ¼ .45) for fretting between the upper (1.3 0.6; range, 1-3) and lower (1.5 0.8; range, 1-4) zones of the stem. Similarly, there was no significant difference (P ¼ 1.0) between the upper and lower zones of the head (both zones 1.3 0.4; range, 1-2). There was, however, strong correlation (r ¼ 0.79; P < .001) for fretting in the upper zones between the head and stem. There was no significant correlation in the lower zone (P ¼ .24) or between the fretting scores and implantation time (P ¼ .71 for the head, P ¼ .64 for the stem) or for patient gender (P ¼ .58 for the head, P ¼ .19 for the stem). There were also no correlations between fretting scores and corrosion scores for either the head (P ¼ .67) or the stem (P ¼ .14). There was only 1 instance of an implant with severe corrosion (score of 4) and 2 instances with moderate corrosion (score of 3). All 3 were the Tornier Aequalis, the most prevalent implant in the study. The severe case was implanted in a male patient for 8.1 years and scored severe for corrosion in both the upper and lower zones of the head
Figure 2 Tribocorrosion damage within the female taper of a head (A), the male taper of a stem (B), and a modular connector between the head and stem (C).
(Fig. 2, A), but it had no visible fretting. This particular implant was revised because of aseptic loosening of the glenoid. The stem was not available. The first moderate case was implanted in a female patient for 11.5 years and scored moderate for corrosion in both the upper and lower
4 zones of the head. As with the severe case, there was no visible fretting, and the stem was unavailable. The glenoid was revised for aseptic loosening. The second moderate case was implanted for 2.1 years and was revised for a rotator cuff tear with glenoid erosion. The implant scored moderate for corrosion in both the upper and lower zones of the head, with no visible fretting. The stem had no visible corrosion in either zone or visible fretting in the upper zone, but it did have mild fretting in the lower zone (Fig. 2, B). There were 2 DePuy AP implants in the study that use a connector between the head and stem (Fig. 2, C). The first case was implanted in a male patient for 0.5 year and had no evidence of corrosion on the connector, but it had mild fretting on both the head and stem sides. This implant was explanted because of infection. The second case was implanted in a female patient for 0.7 year and was revised because of implant instability. This implant had mild corrosion on the head side of the connector but no corrosion on the stem side and had no visible signs of fretting on either connector side. Comparing the stemmed to stemless designs, corrosion was present (score of 2) on 9 of the 24 stemmed design heads (38%) but none of the stemless design heads. On the stems, corrosion was present on 8 of the 20 stemmed design stems (40%) and 1 of the 4 stemless design stems (25%). Fretting was present (score of 2) on 9 of the 24 stemmed design heads (38%) and 1 of the 4 (25%) stemless design heads. On the stems, fretting was present on 10 of the 20 stemmed design stems (50%) and 1 of the 4 stemless design stems (25%). There was no significant difference in the average corrosion score between the stemmed designs and the stemless designs for the heads (P ¼ .29 upper and lower zones) or the stems (P ¼ .43 upper zone, P ¼ .59 lower zone). There was also no significant difference in the average fretting score between the stemmed designs and the stemless designs for the heads (P ¼ .99 upper zone, P ¼ .23 lower zone) or for the stems (P ¼ .75 upper zone, P ¼ .20 lower zone).
Discussion Corrosion was found on 32% of the retrieved heads and 38% of the retrieved stems. However, the majority of these cases were mild, covering <30% of the taper surface within the upper or lower zone. There were only 2 cases with moderate corrosion and 1 case with severe corrosion. Interestingly, corrosion was greater in the lower zone of the stem. Although there was less corrosion on the heads than on the stems, there was a moderate correlation between stem corrosion and head corrosion within the lower zone. There was no correlation between fretting and corrosion, which could potentially be due to the corrosion damage obscuring the fretting marks over time. Two of the 3 most corroded heads were also instances in which the stem
M.G. Teeter et al. was unavailable as it was retained during the revision procedure. That the majority of retrievals had no corrosion or only mild corrosion agrees with our hypothesis and the work of Cusick et al,5 who found mild corrosion on 1 reverse shoulder implant and no corrosion on 4 others. This is a lower incidence than reported for retrieved hip implants, for which corrosion has been found in up to 84% of both metalmetal and ceramic-metal taper interfaces.10 That corrosion was greatest within the lowest zone of the taper connection also agrees with previous studies of retrieved hip implants with varying taper designs.12 This lowest zone of the taper experiences torques that could potentially disrupt the oxide passivity film that forms on alloy surfaces and prevents transportation of metal ions, thus preventing oxidation.13 The lowest zone is also exposed to the oxygen-rich synovial fluid. Both of these are factors that could result in increased corrosion. The numbers of individual implant models included in the study do not enable a comparison of the effect of design factors on the presence of tribocorrosion. The majority of designs had a male taper on the stem side and a female taper on the head side. However, this was reversed for 1 implant, and 1 design uses a separate double-ended connector that fits within female tapers on both the stem and head side (DePuy AP). Although this type of ‘‘dual modularity’’ has had negative effects in some types of hip implants,4,6,11,14 our results indicate that at short-term assessment, the damage findings are not severe in the shoulder. Of the 2 cases that used this style of connector, 1 had mild fretting and 1 had mild corrosion, but neither had signs of moderate or severe tribocorrosion. Comparing the 4 stemless designs to the stemmed designs, no significant differences were found between the mean damage scores. There are a number of limitations with this study. As with all retrieval studies, the implants analyzed have failed and may not be representative of well-functioning implants that remain implanted. None of the implants were revised for trunnionosis. The implants studied include a broad range of designs, models, materials, and sizes as well as different types of modular connections. However, this study represents one of the first instances in which tribocorrosion has been evaluated for shoulder implants of any type. The only previous study examining shoulder implant tribocorrosion was for 5 reverse shoulder implants across 2 different designs.
Conclusion Tribocorrosion was present on the heads and stems of some of the retrieved shoulder implants examined in this study. The incidence of this damage is lower than in previously reported cases of retrieved hip implants. The greatest damage was in the lower zone of the taper,
Tribocorrosion in shoulder arthroplasty where the connection may be exposed to the surrounding joint fluid, consistent with findings in the hip. Whereas tribocorrosion may occur at the modular connections of shoulder implants, it remains to be seen whether this leads to any clinical presentation of trunnionosis. For this study, there were no cases in which the damage was linked to trunnionosis in the patient from whom the implant was retrieved.
Disclaimer Gilles Walch received royalties from Tornier Inc., which is related to the subject of this work. No company had any input into the study design, protocol, testing, data analysis, or manuscript preparation. George S. Athwal is a consultant for DePuy-Synthes and Tornier Inc. In addition, he has received research support from Tornier, DePuy-Synthes, and Exactech for research related to the subject of this article. No company had any input into the study design, protocol, testing, data analysis, or manuscript preparation. The other authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Arnholt CM, MacDonald DW, Tohfafarosh M, Gilbert JL, Rimnac CM, Kurtz SM, et al. Mechanically assisted taper corrosion in modular TKA. J Arthroplasty 2014;29:205-8. http://dx.doi.org/10. 1016/j.arth.2013.12.034 2. Berry DJ, Abdel MP, Callaghan JJ. What are the current clinical issues in wear and tribocorrosion? Clin Orthop Relat Res 2014;472:3659-64. http://dx.doi.org/10.1007/s11999-014-3610-1
5 3. Cooper HJ, Della Valle CJ, Berger RA, Tetreault M, Paprosky WG, Sporer SM, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg Am 2012;94:1655-61. http://dx.doi.org/10.2106/JBJS.K. 01352 4. Cooper HJ, Urban RM, Wixson RL, Meneghini RM, Jacobs JJ. Adverse local tissue reaction arising from corrosion at the femoral neck-body junction in a dual-taper stem with a cobalt-chromium modular neck. J Bone Joint Surg Am 2013;95:865-72. http://dx.doi. org/10.2106/JBJS.L.01042 5. Cusick MC, Hussey MM, Steen BM, Hartzler RU, Clark RE, Cuff DJ, et al. Glenosphere dissociation after reverse shoulder arthroplasty. J Shoulder Elbow Surg 2015;24:1061-8. http://dx.doi.org/10.1016/j. jse.2014.12.019 6. Dunbar MJ. The proximal modular neck in THA: a bridge too far: affirms. Orthopedics 2010;33:640. http://dx.doi.org/10.3928/01477 447-20100722-30 7. Esposito CI, Wright TM, Goodman SB, Berry DJ. What is the trouble with trunnions? Clin Orthop Relat Res 2014;472:3652-8. http://dx.doi. org/10.1007/s11999-014-3746-z 8. Goldberg JR, Gilbert JL, Jacobs JJ, Bauer TW, Paprosky W, Leurgans S. A multicenter retrieval study of the taper interfaces of modular hip prostheses. Clin Orthop Relat Res 2002;401:149-61. 9. Jacobs JJ, Cooper HJ, Urban RM, Wixson RL, Della Valle CJ. What do we know about taper corrosion in total hip arthroplasty? J Arthroplasty 2014;29:668-9. http://dx.doi.org/10.1016/j.arth.2014. 02.014 10. Kurtz SM, Kocagoz SB, Hanzlik JA, Underwood RJ, Gilbert JL, MacDonald DW, et al. Do ceramic femoral heads reduce taper fretting corrosion in hip arthroplasty? A retrieval study. Clin Orthop Relat Res 2013;471:3270-82. http://dx.doi.org/10.1007/s11999-013-3096-2 11. Lanting BA, Teeter MG, Vasarhelyi EM, Ivanov TG, Howard JL, Naudie DD. Correlation of corrosion and biomechanics in the retrieval of a single modular neck total hip arthroplasty design: modular neck total hip arthroplasty system. J Arthroplasty 2015;30:135-40. http://dx. doi.org/10.1016/j.arth.2014.06.009 12. Tan SC, Teeter MG, Del Balso C, Howard JL, Lanting BA. Effect of taper design on trunnionosis in metal on polyethylene total hip arthroplasty. J Arthroplasty 2015;30:1269-72. http://dx.doi.org/10. 1016/j.arth.2015.02.031 13. Wassef AJ, Schmalzried TP. Femoral taperosis: an accident waiting to happen? Bone Joint J 2013;95-B:3-6. http://dx.doi.org/10.1302/0301620X.95B11.32630 14. Wilson DA, Dunbar MJ, Amirault JD, Farhat Z. Early failure of a modular femoral neck total hip arthroplasty component: a case report. J Bone Joint Surg Am 2010;92:1514-7. http://dx.doi.org/10.2106/ JBJS.I.01107
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Tribocorrosion in shoulder arthroplasty humeral component retrievals Matthew G. Teeter, PhDa,b,c, Michael J. Carroll, MD, FRCSCd, Gilles Walch, MDe, George S. Athwal, MD, FRCSCa,d,* a
Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada b Department of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada c Surgical Innovation Program, Lawson Health Research Institute, London, ON, Canada d Roth j McFarlane Hand and Upper Limb Centre, St. Joseph’s Health Care, London, ON, Canada e H^ opital Prive Jean Mermoz, Generale de Sante, Centre Orthopedique Santy, Lyon, France Background: Tribocorrosion at the modular taper connections of total hip implants has been associated with trunnionosis and adverse local tissue reactions. Modularity is also widely used in shoulder arthroplasty implants, but little information exists about the potential for tribocorrosion. This study hypothesized that there would be mild or no tribocorrosion in a series of retrieved shoulder implants. Methods: A total of 28 implants with a mean implantation time of 6.2 6.0 years were evaluated using a validated damage scoring method. Implant tapers on the head and stem were divided into upper (deepest) and lower zones and independently scored for fretting and corrosion damage from 1 (none) to 4 (severe). Results: Corrosion was present on 32% of heads and 38% of stems, whereas fretting was present on 36% of heads and 46% of stems. There was significantly greater (P ¼ .02) corrosion in the lower zone of the retrieved stems (1.4 0.5) than there was in the upper zone (1.1 0.3). Correlation between the head and stem corrosion for lower zone was moderate (r ¼ 0.41; P ¼ .04). Discussion: Tribocorrosion was present on the heads and stems of some of the retrieved shoulder implants examined in this study. The incidence of tribocorrosion in shoulder implants was lower than in reported cases of retrieved hip implants. The greatest damage was in the lower zone of the taper, where the connection may be exposed to the surrounding joint fluid. It remains to be seen whether this leads to any clinical presentation of trunnionosis. Level of evidence: Basic Science Study, Implant Retrieval. Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Shoulder arthroplasty; humeral component; revision; tribocorrosion; fretting; corrosion; trunnionosis; retrieval
Investigations performed at the Implant Retrieval and Analysis Laboratory, University of Western Ontario, London, ON, Canada. IRB approval was not required for this study. *Reprint requests: George S. Athwal, MD, FRCSC, Roth j McFarlane Hand and Upper Limb Centre, St. Joseph’s Health Care, 268 Grosvenor St, London, ON N6A 4L6, Canada. E-mail address: [email protected] (G.S. Athwal).
Modularity in joint replacement implants enables the arthroplasty surgeon to customize the fit of an implant to the patient intraoperatively. Recently, the modular connectors between implant components have been identified as a source of corrosion and debris, leading to so-called trunnionosis.2-4,7,9 Trunnionosis is the term used to describe
1058-2746/$ - see front matter Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2015.07.004
2 the clinical symptoms caused by tribocorrosion, which is damage to the Morse taper connections of modular joint replacements. This damage is made up of fretting, seen as scars in the metal surface, and corrosion, seen as black debris. First identified with metal-on-metal total hip implants, tribocorrosion in taper junctions has now also been identified in metal-on-plastic total hip implants and in modular total knee replacement.1,12 Many different factors are thought to be associated with tribocorrosion, including head size, head offset, head angle, flexural rigidity of the neck, dissimilar alloy pairings, and dimensions of the modular taper connection itself.7 Modularity is also widely used in shoulder arthroplasty implants. However, retrieval studies of shoulder implants are much sparser in the literature than for hip or knee implants. Cusick et al5 studied dissociation of reverse total shoulder replacement implants and were able to evaluate 5 retrieved implants using tribocorrosion damage scoring. Four of the 5 implants had no signs of fretting or corrosion at the modular connection, and 1 implant had mild fretting and corrosion. In this 1 implant, the corrosion was only a small area of damage and did not cause any permanent deformation of the taper. Our institution has a long-running implant retrieval program for the hip and the knee and has subsequently expanded to include the shoulder. We have used our retrieval program to evaluate tribocorrosion of hip implants associated with factors such as dual-modular stems, trunnion size, and head length. The purpose of this study was to evaluate the presence of tribocorrosion in retrieved humeral total and hemiarthroplasty modular implants. We hypothesized that we would see mild or no corrosion or fretting damage at the modular connections of shoulder arthroplasty retrieval implants.
Methods Twenty-eight implants explanted by 2 shoulder surgeons (G.S.A., G.W.) were available for analysis. All implants were used in anatomic total shoulder arthroplasty or hemiarthroplasty. The implants had a mean implantation time of 6.2 6.0 years (range, 0.4-21 years). Implants were used in 11 male patients and 17 female patients. The primary reason for revision was glenoid or humeral component loosening for 11 cases, rotator cuff tear for 8 cases, infection for 5 cases, instability for 2 cases, and pain and malpositioning for 1 case each. No cases were revised for known trunnionosis. The implant models included Aequalis (Tornier, Bloomington, MN, USA; n ¼ 13), Bigliani/Flatow (Zimmer, Warsaw, IN, USA; n ¼ 3), Univers II (Arthrex, Naples, FL, USA; n ¼ 2), AP (DePuy, Warsaw, IN, USA; n ¼ 2), Eclipse (Arthrex; n ¼ 1), Bio-Modular (Biomet, Warsaw, IN, USA; n ¼ 1), Nano (Biomet; n ¼ 1 ), TESS (Biomet; n ¼ 1), Unite (DePuy; n ¼ 1), Reunion (Stryker, Kalamazoo, MI, USA; n ¼ 1), Solar (Stryker; n ¼ 1), and Sidus (Zimmer; n ¼ 1). All models included a cobalt-chromium humeral head and a titanium humeral stem or anchor.
M.G. Teeter et al.
Figure 1 Diagram of a shoulder replacement implant, showing the upper and lower zones that were assigned to the modular connectors of the head and stem (inset).
The visual damage classification score for fretting and corrosion described by Goldberg et al8 was used for this study. This classification is the most commonly used damage scoring system to identify tribocorrosion on retrieved implants. Fretting and corrosion are scored independently, ranging from 1 (none) to 4 (severe). For corrosion, a mild score of 2 represents <30% of the taper surface being discolored or dull, whereas a moderate score of 3 represents discoloration of >30% of the surface or the presence of black debris, pits, or etch marks over <10% of the surface. A severe corrosion score of 4 represents >10% of the surface containing black debris, pits, or etch marks. For fretting, a mild score of 2 represents bands of scars involving 3 or fewer machine lines, and a moderate score of 3 represents the involvement of >3 machine lines. A severe score of 4 involves several bands of scars across multiple adjacent machine lines or flattened areas with nearby scars. Iatrogenic damage from implantation or explantation was identified and excluded from the tribocorrosion assessment. Two observers analyzed each retrieved implant independently and recorded a score using the damage scale. In the case of a scoring discrepancy, both observers reanalyzed the implant and decided on a mutually agreeable value. All analyses were performed using a stereomicroscope (SZ-CTV; Olympus, Tokyo, Japan). The modular connections of the head and stem were divided in half into upper and lower zones, representing the deepest and most exposed regions of the taper connections, respectively (Fig. 1). Therefore, for each implant, a total of 8
Tribocorrosion in shoulder arthroplasty
3
scores were assigned: a fretting score and corrosion score for the upper and lower zones for both the head and the stem. Two implants used a separate connector part between the head and the stem, for which an additional 4 scores were recorded (fretting and corrosion scores for the head side and the stem side). In 1 case, the stem had a female taper, whereas in all other instances, the stem had a male taper. In a minority of cases (n ¼ 4), only the humeral heads were explanted and the stems remained in situ and therefore were unavailable. Descriptive statistics were calculated for all measurements. A D’Agostino and Pearson normality test revealed a non-Gaussian distribution for the data. Therefore, a Wilcoxon matched-pairs signed rank test was used to compare values for fretting and corrosion between zones, and the Spearman rank correlation coefficient was used for correlations between values. A P value of <.05 was considered significant. All statistical analysis was performed with Prism version 6.0 (GraphPad Software Inc., La Jolla, CA, USA).
Results Corrosion was present (score of 2) on 9 of the 28 heads (32%) and 9 of the 24 stems (38%). There was significantly greater (P ¼ .02) corrosion in the lower zone of the retrieved stems (1.4 0.5; range, 1-2) than there was in the upper zone (1.1 0.3; range, 1-2). However, there was no difference (P ¼ 1.0) in corrosion scores between the upper and lower zones of the retrieved heads (both zones 1.4 0.8; range, 1-4). The correlation for lower zone corrosion between the head and stem was moderate (r ¼ 0.41; P ¼ .04); but for the upper zone, it was insignificant (r ¼ 0.10; P ¼ .63). There were no significant correlations between corrosion scores and implantation time (P ¼ .10 for the head, P ¼ .31 for the stem) or for patient gender (P ¼ .17 for the head, P ¼ .54 for the stem). Fretting was present (score of 2) on 10 of the 28 heads (36%) and 11 of the 24 stems (46%). There was no significant difference (P ¼ .45) for fretting between the upper (1.3 0.6; range, 1-3) and lower (1.5 0.8; range, 1-4) zones of the stem. Similarly, there was no significant difference (P ¼ 1.0) between the upper and lower zones of the head (both zones 1.3 0.4; range, 1-2). There was, however, strong correlation (r ¼ 0.79; P < .001) for fretting in the upper zones between the head and stem. There was no significant correlation in the lower zone (P ¼ .24) or between the fretting scores and implantation time (P ¼ .71 for the head, P ¼ .64 for the stem) or for patient gender (P ¼ .58 for the head, P ¼ .19 for the stem). There were also no correlations between fretting scores and corrosion scores for either the head (P ¼ .67) or the stem (P ¼ .14). There was only 1 instance of an implant with severe corrosion (score of 4) and 2 instances with moderate corrosion (score of 3). All 3 were the Tornier Aequalis, the most prevalent implant in the study. The severe case was implanted in a male patient for 8.1 years and scored severe for corrosion in both the upper and lower zones of the head
Figure 2 Tribocorrosion damage within the female taper of a head (A), the male taper of a stem (B), and a modular connector between the head and stem (C).
(Fig. 2, A), but it had no visible fretting. This particular implant was revised because of aseptic loosening of the glenoid. The stem was not available. The first moderate case was implanted in a female patient for 11.5 years and scored moderate for corrosion in both the upper and lower
4 zones of the head. As with the severe case, there was no visible fretting, and the stem was unavailable. The glenoid was revised for aseptic loosening. The second moderate case was implanted for 2.1 years and was revised for a rotator cuff tear with glenoid erosion. The implant scored moderate for corrosion in both the upper and lower zones of the head, with no visible fretting. The stem had no visible corrosion in either zone or visible fretting in the upper zone, but it did have mild fretting in the lower zone (Fig. 2, B). There were 2 DePuy AP implants in the study that use a connector between the head and stem (Fig. 2, C). The first case was implanted in a male patient for 0.5 year and had no evidence of corrosion on the connector, but it had mild fretting on both the head and stem sides. This implant was explanted because of infection. The second case was implanted in a female patient for 0.7 year and was revised because of implant instability. This implant had mild corrosion on the head side of the connector but no corrosion on the stem side and had no visible signs of fretting on either connector side. Comparing the stemmed to stemless designs, corrosion was present (score of 2) on 9 of the 24 stemmed design heads (38%) but none of the stemless design heads. On the stems, corrosion was present on 8 of the 20 stemmed design stems (40%) and 1 of the 4 stemless design stems (25%). Fretting was present (score of 2) on 9 of the 24 stemmed design heads (38%) and 1 of the 4 (25%) stemless design heads. On the stems, fretting was present on 10 of the 20 stemmed design stems (50%) and 1 of the 4 stemless design stems (25%). There was no significant difference in the average corrosion score between the stemmed designs and the stemless designs for the heads (P ¼ .29 upper and lower zones) or the stems (P ¼ .43 upper zone, P ¼ .59 lower zone). There was also no significant difference in the average fretting score between the stemmed designs and the stemless designs for the heads (P ¼ .99 upper zone, P ¼ .23 lower zone) or for the stems (P ¼ .75 upper zone, P ¼ .20 lower zone).
Discussion Corrosion was found on 32% of the retrieved heads and 38% of the retrieved stems. However, the majority of these cases were mild, covering <30% of the taper surface within the upper or lower zone. There were only 2 cases with moderate corrosion and 1 case with severe corrosion. Interestingly, corrosion was greater in the lower zone of the stem. Although there was less corrosion on the heads than on the stems, there was a moderate correlation between stem corrosion and head corrosion within the lower zone. There was no correlation between fretting and corrosion, which could potentially be due to the corrosion damage obscuring the fretting marks over time. Two of the 3 most corroded heads were also instances in which the stem
M.G. Teeter et al. was unavailable as it was retained during the revision procedure. That the majority of retrievals had no corrosion or only mild corrosion agrees with our hypothesis and the work of Cusick et al,5 who found mild corrosion on 1 reverse shoulder implant and no corrosion on 4 others. This is a lower incidence than reported for retrieved hip implants, for which corrosion has been found in up to 84% of both metalmetal and ceramic-metal taper interfaces.10 That corrosion was greatest within the lowest zone of the taper connection also agrees with previous studies of retrieved hip implants with varying taper designs.12 This lowest zone of the taper experiences torques that could potentially disrupt the oxide passivity film that forms on alloy surfaces and prevents transportation of metal ions, thus preventing oxidation.13 The lowest zone is also exposed to the oxygen-rich synovial fluid. Both of these are factors that could result in increased corrosion. The numbers of individual implant models included in the study do not enable a comparison of the effect of design factors on the presence of tribocorrosion. The majority of designs had a male taper on the stem side and a female taper on the head side. However, this was reversed for 1 implant, and 1 design uses a separate double-ended connector that fits within female tapers on both the stem and head side (DePuy AP). Although this type of ‘‘dual modularity’’ has had negative effects in some types of hip implants,4,6,11,14 our results indicate that at short-term assessment, the damage findings are not severe in the shoulder. Of the 2 cases that used this style of connector, 1 had mild fretting and 1 had mild corrosion, but neither had signs of moderate or severe tribocorrosion. Comparing the 4 stemless designs to the stemmed designs, no significant differences were found between the mean damage scores. There are a number of limitations with this study. As with all retrieval studies, the implants analyzed have failed and may not be representative of well-functioning implants that remain implanted. None of the implants were revised for trunnionosis. The implants studied include a broad range of designs, models, materials, and sizes as well as different types of modular connections. However, this study represents one of the first instances in which tribocorrosion has been evaluated for shoulder implants of any type. The only previous study examining shoulder implant tribocorrosion was for 5 reverse shoulder implants across 2 different designs.
Conclusion Tribocorrosion was present on the heads and stems of some of the retrieved shoulder implants examined in this study. The incidence of this damage is lower than in previously reported cases of retrieved hip implants. The greatest damage was in the lower zone of the taper,
Tribocorrosion in shoulder arthroplasty where the connection may be exposed to the surrounding joint fluid, consistent with findings in the hip. Whereas tribocorrosion may occur at the modular connections of shoulder implants, it remains to be seen whether this leads to any clinical presentation of trunnionosis. For this study, there were no cases in which the damage was linked to trunnionosis in the patient from whom the implant was retrieved.
Disclaimer Gilles Walch received royalties from Tornier Inc., which is related to the subject of this work. No company had any input into the study design, protocol, testing, data analysis, or manuscript preparation. George S. Athwal is a consultant for DePuy-Synthes and Tornier Inc. In addition, he has received research support from Tornier, DePuy-Synthes, and Exactech for research related to the subject of this article. No company had any input into the study design, protocol, testing, data analysis, or manuscript preparation. The other authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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